Pick resistant lock

ABSTRACT

A pick resistant lock having a housing and a rotatable spindle therewithin, each having a registrable aperture. Interposed between the housing and spindle is a ring that is rotatable relative to said housing a limited distance and has an aperture registrable with said housing and spindle apertures. A tumbler is disposed in said registrable apertures and is biased to a normal position in which said spindle and ring must move together. When the spindle is torqued to pick the lock, the spindle and ring will rotate said limited distance to permit the apertures therein, and the tumbler, to move out of register with said housing aperture and thus prevent the unlocking of the lock. The tumbler is further provided with a chamfered end so that it cannot be felt when the tumbler moves into said housing aperture.

o United States Patent 1 [111 3,73,000 Gill Jan. 8, 1974 PICK RESISTANTLOCK Primary ExaminerR0bert L. Wolfe 75 Inventor: Vincent A. Gill,Montclair, NJ.

[73] Assignee: Unican Security Systems, Ltd,

Montreal, Canada [57] ABSTRACT [22] Filed: Apr. 20; 11972 A pickresistant lock having a housing and a rotatable 21 A L N 245 73 spindletherewithin, each havlng a registrable aper- 1 0 6 ture. interposedbetween the houslng and spindle is a ring that is rotatable relative tosaid housing a limited [52] US. Cl. 70/363, 70/419 di tance and has anaperture registrable with said [51] Int. Cl EOSb 27/08, EOSb 63/00housing and spindle apertures. A tumbler is disposed [5 Field Of ar 364in said registrable apertures and is biased to a normal 70/364 378position in which said spindle and ring must move together. When thespindle is torqued to pick the lock, References Cited the spindle andring will rotate said limited distance to UNITED STATES PATENTS permitthe apertures therein, and the tumbler, to move 3,045,468 7/1962Welch..'; 70/364 A out of register with said housing aperture and thus047 4 3 2 1912 'Aguenbmun 70 3 4 A prevent the unlocking Of the lOCk.The tumbler lS fur- 3,656,328 4/1972 Hughes 70/276 ther Provided with aChamfefed end 50 that it Cannot 1,6l9,252 3/1927 George 70/363 be feltwhen the tumbler moves into said housing ap- 3,541,819 ll/l97O Kerr70/363 ertul'e.

3,3l9,443 5/1967 Perlick 70/42l 3 Claims, 6 Drawing Figures FALSE 60 a 2-6 SHEAR PLANE-- E SHEAR PLANE E 6 TRUE PAIENTEDJAM elm 3,783,660

sum 1 OF 2 n ,TRuE SHEAR PLANE FALSE SHEAR PLANE! E TRUE SHEAR PLANEPATENTED 8W4 3,783,660

1/2 FALSE ISHEAR 4'6 TRUZ I SHEAR PLANE PICK RESISTANT Loc BACKGROUND OFTHE INVENTION Field of the Invention This invention relates to looksand, more particularly, to locks containing one or more pick resistantfeatures.

Normal (non-master) locks have a relatively rotatable spindle andhousing with normally aligned apertures and a tumbler in said aperturesbridging the spindie and housing to prevent relative rotation. The keymoves the tumbler to free the spindle and thus permit unlocking. Amaster lock interposes a ring between said spindle and housing toprovide an additional master key unlocking position in which the spindleand ring are held together by the tumbler but both are free to rotaterelative to the housing.

SUMMARY OF THE INVENTION The pick resistant lock of this inventioncomprises a spindle rotatably mounted within a housing with a ringpositioned about the spindle between the housing and spindle; Thehousing, ring and spindle each have an opening therein, which openingsare normally aligned when the lock is locked.

This invention makes use of a three-pin set of tumbler pins. A firsttumbler pin of each set is normally positioned in an associated openingin the housing with its outer end at a false shear plane between thering and housing and its inner end abutting a standard compressionspring disposed within said housing opening. A second tumbler pin ofeach set is normally positioned in an associated opening in the ringwith its inner end normally in contact with the outer end of the firsttumbler pin at the false shear plane and its outer end normally withinthe' associated spindle opening. Further, a third thumbler pin of eachset is normally positioned in an associated opening in the spindle withan inner end in contact with the second tumbler pin and an outer endaccessible to a key. Thus, in the normal condition the spindle is freeto rotate with the ring along the unobstructed false shear plane.

However, means areprovided for allowing only a limited rotation of thering relative to the housing. The extent of such limited rotation issufficient to misalign the ring openings with the housing cavities, butinsufficient to open the look. When the spindle isrotated as far aspermitted, the openings of the ring will be misaligned with the openingsin the housing so that the tumbler pins ,of each set cannot be pushedtoward the associated spring to advance the inner end of the thirdtumbler pin to the true shear plane, which is required to open the lock.Thus, the lock cannot be picked.

In a further aspect of this invention, means are included for insuringsubstantially unobstructed axial movement of the third tumbler pin ofeach set at least part of the way into the associated openings in thering when the lock is in its normal locked position. In this manner, thepicker is prevented from sensing or feeling the arrival of the inner endof each third tumbler pin at the true shear plane. Thus, even if thepicker initially attempts to push the third tumbler pins to the trueshear plane before applying torque, it will be substantially impossiblefor him to sense at what point such pins actually are at the true shearplane.

' These and other aspects and advantages of this invention shall be moreclearly described below with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-sectional view of acylindrical key lock embodying this invention;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view similar to FIG. 1 but showing a keyinserted therein:

FIG. 4 is a cross-sectional view of a flat key lock embodying thisinvention;

FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 4; and

FIG. 6 is a cross-sectional view similar to FIG. 4 but showing a keyinserted therein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring. to FIG. 1, a pickresistant lock 10 of this invention is shown. Look 10 includes acylindrical housing 11 defined by a cylindrical shell 12 and an annularheader 20. Shell 12 is preferably fabricated of a suitable metal and hasan interior cylindrical chamber 14 therein. Chamber 14 extends between apair of opposing opened ends ]l6 and 18, respectively. Header 20, alsopreferably fabricated of metal, is mounted within chamber 114 at end 18thereof and extends in a direction parallel to the axis of shell 12 fromend 18 of chamber 14 to a point within chamber 14 approximatelyintermediate ends 16 and 18 thereof. Header 20 is fixed in positionrelative to shell 12 by a pin 22 which is inserted through alignedopenings 24 and 26 defined in shell 12 and header 20, respectively.

Header 20 further includes a restraining pin 28 which is fitted within acorresponding aperture 29 in the header and which has a forward end 30extending a predetermined distance from an outer end 32 of header 20.The purpose of pin 28 will be described in more detail below. Header 20further includes a plurality of elongate cavities 34 each extendingsubstantially parallel to the longitudinal axis of shell 12. Thecavities 34 are preferably spaced uniformly about the header. Lock 10further includes a ring 36 (FIGS. 1 and 2) which is rotatably mountedabout a spindle 44 which is positioned for rotation within chamber 14with an inner end 38 abutting outer end 32 of header 20 and an outer end48 of the ring abutting a peripheral flange 46 of the spindle. Ring 36further includes a plurality of openings 40 each extending through thering in a direction substantially parallel to the axis of the housingshell when the ring is disposed within the shell about spindle 44.Openings 40 are equal in number to, and are registrable with cavities 34in header 20.

It is preferred that header 20 contain seven cavities 34 and with sevencorresponding openings 40 being formed in ring 36 wherein the cavitiesand openings are each spaced at approximately 45 intervals relative toeach other about the header and ring, respectively. This leaves a gap ofapproximately between one adjacent pair of cavities 34 and one adjacentpair of openings 40. In accordance with this invention, a slot 42 isprovided in end 38 of ring 36 at a location on said ring within theabove mentioned 90 gap thereon. Spindle 44 is positioned in chamber 14with end 30 of pin 23 received within slot 42, the length of pin 28being sufficient for this purpose. It is important that the diameter ofpin 28 be less than the width of slot 42. Preferably,

the diameter of pin 28 is approximately about one-half the width of slot42.

Thus, pin 28 and milled slot 42 on ring 36 provide a means forpermitting limited rotation of ring 36 about its axis and relative tohousing 11. More specifically, ring 36 may be rotated in eitherdirection, but only until a side of slot 42 engages pin 28. For purposesof future explanation, the interface between end 38 of ring 36 and end32 of heading 20 shall be referred to as the false shear plane" of lock10.

Spindle 44 is preferably circularly cylindrical in shape having a mainshaft 45 and peripheral flange 46 which is also preferably annular inshape. The diameter of flange 46 is slightly less than the innerdiameter of shell 12, whereas the spindle shaft has a diameter slightlyless than the inner diameter of header 20. In this manner, spindle 44 isnormally rotatable within chamber 14 relative to housing shell 12 andring 36. In the future, the interface between flange 46 and ring 36shall be referred to as the true shear plane of lock 10.

In accordance with this invention, flange 46 of spindle 44 includes aplurality of apertures 50, preferably seven, extending therethrough in adirection substantially parallel to the axis of shell 12. Apertures 50are spaced identically as openings 40 in ring 36 and are normallyaligned with said openings.

Look further includes a plurality of tumbler pin sets equal in number tothe number of cavities 34 in header 20. Each tumbler pin set includes afirst tumbler pin 60 which is normally positioned entirely within acorresponding cavity 34 with an inner end 62 thereof abutting spring 58and an outer end 64 thereof normally located at the false shear plane.Each tumbler pin set additionally includes a second tumbler pin 66 whichis nonnally positioned in a corresponding opening of ring 36 with aninner end 68 thereof abutting outer end 64 of first tumbler pin 60, andan outer end 70 thereof disposed within an aligned aperture 50 ofspindle flange 46. Lastly, each tumbler pin set includes a third tumblerpin 72 which is positioned within said aligned aperture 50 of spindleflange 46 with an inner end 74 thereof abutting outer end 70 of secondtumbler pin 66, and an outer end 76 thereof located near end 16 ofchamber 14. Suitable biasing means such as springs 58 are employed tourge the tumbler pin sets to their normal positions. However, otherbiasing means, such as gravity or magnetics, may be employed.

Thus, in the normal locked position of lock 10, the outer end 64 of eachfirst tumbler pin 60, as well as the inner end 68 of each second tumblerpin 66 are located at the false shear plane so that ring 36 may berotated relative to housing 11 (Le. header and shell 12). However, aspointed out above, such rotation may be effected only to the extent thatpin 28 is free from engagement with the side walls of slot 42 of ring36. Further, and in the normal position of lock 10, spindle 44 may notbe rotated freely relative to ring 36, inasmuch as second tumbler pins66 are disposed within apertures 50 of spindle flange 46 as well asopenings 40 of ring 36. Thus, in attemptingto pick the lock the spindle44 will be torqued and this will cause simultaneous rotation of thespindle and ring 36. However, rotation of spindle 44 will be limited dueto the cooperation of pin 28 in milled slot 42 of ring 36. Thesignificance of the above limited rotation will be explained below.

Referring to FIG. 3, the manner of opening lock 10 with a conventionalcylindrical key 78 will be described. Key 78 includes an annular shaft80 which is dimensioned for receipt within annular slot 54 definedbetween shell 12 and spindle 44.

Key 78 further includes a plurality of grooves 88 respectivelyassociated with the plurality of tumbler pin sets. The grooves areprovided in the outer surface of key shaft 80 at a location near theforward end of the key with the relative spacing between the groovesbeing identical as that between the tumbler pin sets so as to bealignable with said sets when the key is inserted in lock 10. Inaddition, key shaft 80 is provided with an indexing flange 82 which,when disposed in indexing slot 56, properly locates each groove 88relative to its associated tumbler pin assembly. Lastly, a flange 84 onthe inside of key shaft 80 fits into keyway 52 on spindle 44.

When shaft 80 of key 78 is inserted into slot 54, end 90 of key 78engages spindle flange 46, whereas a floor 92 of each groove 88 willengage the outer end 76 of the aligned third tumbler pin 72. It will berealized, therefore, that the depth of each groove 88 between end 90 ofthe key and floor 92 of the groove necessarily determine the extent towhich the three tumbler pins of each set will be pushed inwardly throughthe aligned cavity 34, opening 40 and aperture 50 toward the associatedspring 58.

As is conventional in most locks, the tumbler pins of each setpreferably have different aggregate lengths so that each set must bemoved inwardly a different distance before positioning the inner end 74of the third tumbler pin of each set at the true shear plane. Theplurality of grooves 88 of key 78 are thus dimensioned accordingly tobring the inner end of each third tumbler pin into position at the trueshear plane when the key is inserted in the lock. Then, a torque exertedon key 78 will cause rotation of the key and the spindle because flange84 is in spindle keyway 52. Rotation of the spindle is not in any waylimited since the spindle is free of ring 36 and housing 20 at the trueshear plane.

As mentioned before, a person trying to pick a lock usually firstattempts to apply torque to the spindle of the lock. He then operateseach tumbler to move them to the true shear plane whereupon the spindleis free to rotate to open the lock. In accordance with the presentinvention, a lock picker applying torque to spindle 44, such as byinserting a pin in the key slot 52 in the spindle and applying torque tothe spindle, will actually succeed in simultaneously rotating bothspindle 44 and ring 36 a limited distance until pin 28 engages a sidewall of ring 36. At this point, openings 40 in ring 36 will be out ofalignment with cavities 34 of header 20 so that a subsequent attempt topush the tumbler pins inwardly will be prevented Only a very slightrotation of spindle 44 and ring 36 by the picker will cause a sufficientmisalignment between openings 40 and cavities 34 to prevent picking. Asit is very difficult to pick a lock without torquing the spindle, thelock 10 is highly pick resistant. However, if an attempt to pick thelock is made, thus leaving the spindle out of alignment with housing 20,the spindle may easily be realigned for subsequent key operation of thelock.

This invention also seeks to prevent a lock picker from feeling thearrival of the inner end of each third tumbler pins 72 at the true shearplane if he elects to attempt to push the pins inwardly before applyingtorque to spindle 44. Thus, in accordance with this invention, innerends 74 of third tumbler pins 72 are chamfered so that the outerdiameter of each pin 72 at end 74 is substantially less than thediameter of openings 40 in ring 36.

In this manner, the picker will, at best, be able to detect when an edge73, representing the innermost edge of the non-chamfered portion of eachpin 72, arrives at the true shear plane. At this point, the front end 74of each third tumbler pin 72 is disposed well within the opening 40 ofring 36 and not at the true shear plane. Thus, the lock cannot be pickedin this manner either.

Preferably, the inner and outer edges of ring 36 at the periphery ofholes are also chamfered so as to further ensure the non-engagement ofthird tumbler pins 72 with ring 36.

It is to be noted, as mentioned above, that the feature of chamferingthe inner end of the outermost tumbler pin of each set may be applied toany present day lock, in addition to lock of this invention. Forexample, the outer tumbler pin of each tumbler pin set in a conventionalnon-master lock may have its inner end chamfered so as to prevent apicker from sensing the engagement of such end with the shell at theshear plane.

Reference is now had to FIGS. 4-6 wherein another embodiment of a lockof this invention, lock 100 is shown. Lock 100 is specifically designedfor operation with a conventional flat key (such as a flat key 102partially shown in FIG. 6).

Referring now to FIGS. 4 and S in detail, it will be seen that lock 100includes a housing 103 defined by a cylindrical shell 104 which ishollowed out to form an inner cylindrical chamber 106. Chamber 106 ispreferably circularly cylindrical and is preferably positioned eccentricto the longitudinal axis of shell 104. Further, chamber 106 extendsbetween a pair of opposing ends thereof (only outer end 108 of chamber106 being shown). Chamber 106 is thus bounded peripherally by an innerside wall 110 of shell 104. Shell 104 further in cludes an annulargroove 112 formed in inner wall 110 at a location near end 108 ofchamber 106. Groove 112 is dimensioned to receive an annular flange 114of a conventional flat key lock spindle 116 which will be morecompletely described below.

In accordance with thisinvention, an elongate cylindrical ring 1 18 isinserted within chamber 106 with its outer side wall 120 rotatablyfitted against inner side wall 110 of shell 104. Hereinafter, theinterface between ring 1 18 and shell 104 shall be referred to as theflase shear plane. v

Spindle 116 is inserted within chamber 106 through ring 118 with anouter side wall 122 of the spindle being loosely fitted against ring 118for rotation of the spindle in the chamber relativeto the ring.,Asstated above, spindle 116 preferably includes an annular flange 114which is receivedwithin annular groove 112 in shell 104. The interfacebetween spindle side wall 122 and ring 118 shall be referred tohereinafter as the true shear plane. I

. As with lock 10, lock 100 includes a plurality of cavities 126 definedin shell 104 which are alignable with a corresponding plurality ofopenings 128 in ring 118 and with a corresponding plurality of apertures130 in spindle 116. In a flat key lock, cavities126, openings 128 andapertures 130 each-extend elongately in a direction perpendicular to thelongitudinal axis of chamber 106 of shell 104Yand are spaced from oneanother along the longitudinal axis of the lock. Further, a conventionalkey slot 132 (FIG. 5) is provided through the spindle in a directionalong the longitudinal axis of the spindle.

In accordance with the principles of this invention, a set of tumblerpins are provided for each alignable set of cavities 126, openings 128and apertures 130. More specifically, a first tumbler pin 134 isnormally positioned within a corresponding cavity 126 with an outer end136 thereof in contact with a conventional tumbler spring 138, alsopositioned within cavity 126, and an inner end 139 of the pin normallypositioned at the false shear plane. A second tumbler pin 140 isnonnally positioned in a corresponding opening 128 of ring 118 with anouter end 142 of the second tumbler pin at the false shear plane and aninner end 144 of the second tumbler pin within a corresponding andaligned aperture 130 of spindle 116 thereby preventing relative rotationbetween ring 118 and spindle 116. Lastly, a third tumbler pin 146 ofeach set is positioned within a corresponding aperture 130 of spindle116 with an outer end 148 thereof in contact with the second tumbler pinand an inner end 150 of the third tumbler pin disposed within key slot132 at a location thereat preferably intersecting the longitudinal axisof spindle 116.

In accordance with this invention, a segment 152 (FIG. 5) of outer sidewall 120 of ring 118 is slotted to receive a limit pin 156 protrudingthrough an opening 158 in inner side wall 110 of shell 104. Thecooperation of pin 156 and slot 152 is entirely similar to thecooperation between pin 28 and slot 42 of lock 10. In other words, ring118 may be rotated relative to shell 104 only until pin 156 engageseither side of slot 152. Thus, a picker applying torque to the spindleto rotate it will succeed to a limited extent sufficient to misalignopenings 130 with cavities 126. This prevents the picker from manuallypushing in the tumbler pins to position the inner ends of the thirdtumbler pins at the true shear plane.

Also, and as with lock 10, the inner ends 148 of the third tumbler pins146 are preferably chamfered so that a picker may not feel" when suchends arrive at the true shear plane. Thus, if the picker pushes thetumbler pins inwardly, he might push too far bringing the inner end of athird tumbler. pins into an aligned opening 130 so that ring 118 will becaused to rotate along with spindle 116 thereby again limiting rotationuntil pin 156 engages a side wall of 'slot 152. If he doesnt push farenough, the second tumbler pin will cause simultaneous rotation ofspindle 116 and ring 118.

The method of opening lock 100 with a flat key 102 shall be describedwith reference to FIG. 6. As is conventional, flat key 102 includes aplurality of notches 160 cut beneath an upper edge 162 thereof. Thespacing between notches 160 is identical to that between the tumbler pinsets. When key 102 is inserted within key slot 132, the front end of thekey (not shown) will engage seriatim the third tumbler pins of each setforcing each set of tumbler pins toward springs 138. When the keyisfully inserted in slot 132, each third tumbler pin will be nested at itsinner end within corresponding notch 160 of the key. The notches are cutof a depth such that the outer end of each third tumbler pin will bepositioned at the true shear plane. Thus, a

torque exerted on key 102 will cause spindle 116 to rotate freely withinchamber 106 and relative to ring 118 to open the lock.

Although the invention has been described with reference to a number ofspecifically illustrated embodiments, the invention is not to be solimited. Rather, the invention is deemed to include obviousmodifications and changes to the above described embodiments.

For example, a cylindrical key lock may be fabricated with a housingshell and header formed as an integral unit. Thus, reference in theclaims to a housing shall be deemed to include an integral shell/headerunit, as well as separate shell'and header parts (lock 10). Further, theterm housing is deemed to include a shell alone, as in the case of lock100.

Other obvious modifications and changes are contemplated is thisinvention, the precise scope of which is to be defined by the followingclaims.

What is claimed is:

l. A pick resistant lock comprising:

a. a hollow housing having an elongate cavity formed therein;

b. a spindle rotatably mounted within said housing and including anaperture extending therethrough at a location thereon for alignment withsaid cavity;

0. ring means rotatably mounted about the spindle between the spindleand the housing and including an opening extending therethrough at alocation thereon for alignment with said cavity and said aperture, thering means and spindle being normally positioned with said cavity,aperture and opening in alignment, a true shear plane being defined atan interface between the spindle and ring means and a false shear planebeing defined at an interface between the ring means and housing;

(1. a tumbler assembly comprising a first pin positioned in said cavity,said first pin having an outer end normally positioned at said falseshear plane, a second pin normally positioned in said opening with aninner end thereof normally in contact with said first pin at said falseshear plane and an outer end thereof normally within said aperture, athird pin normally positioned in said aperture with an inner end thereofnormally in contact with said second pin, the third pin being accessibleto a key from without the housing, the second pin normally preventingrelative rotational movement between the spindle and ring, and means forbiasing said tumbler'assembly to its normal position;

e. means for allowing only a limited rotation of the ring means relativeto the housing, which limited rotation is sufficient in extent to effecta misalignmerit of the openings in the ring with the cavities in thehousing; and

f. means for enabling substantially unrestrained axial movement of saidthird pin at least part of the way into the opening of said ring means.

2. A pick resistant lock comprising:

a. a hollow housing having an elongate cavity formed therein;

b. a spindle rotatably mounted within said housing and including anaperture extending therethrough at a location thereon for alignment withsaid cavity;

c. ring means rotatably mounted about the spindle between the spindleand the housing and including an opening extending therethrough at alocation thereon for alignment with said cavity and said aperture, thering means and spindle being normally positioned with said cavity,aperture and opening in alignment, a true shear plane being defined atan interface between the spindle and ring means and a false shear planebeing defined at an interface between the ring means and housing;

d. a tumbler assembly comprising a first pin positioned in said cavity,said first pin having an outer end normally positioned at said falseshear plane, a second pin normally positioned in said opening with aninner end thereof normally in contact with said first pin at said falseshear plane and an outer end thereof normally within said aperture, athird pin normally positioned in said aperture with an inner end thereofnormally in contact with said second pin, the third pin being accessibleto a key from without the housing, the second pin normally preventingrelative rotational movement between the spindle and ring, and means forbiasing said tumbler assembly to its normal position;

e. means for allowing only a limited rotation of the ring means relativeto the housing, which limited rotation is sufficient in extent to effecta misalignment of the openings in the ring with the cavities in thehousing; and

f. wherein the cavity, aperture and opening each extend elongately in adirection parallel to the longitudinal axis of the housing.

3. The lock of claim 1, wherein the enabling means includes the innerend of said third tumbler pin being chamfered to an outer diametersubstantially less than the diameter of said opening.

1. A pick resistant lock comprising: a. a hollow housing having anelongate cavity formed therein; b. a spindle rotatably mounted withinsaid housing and including an aperture extending therethrough at alocation thereon for alignment with said cavity; c. ring means rotatablymounted about the spindle between the spindle and the housing andincluding an opening extending therethrough at a location thereon foralignment with said cavity and said aperture, the ring means and spindlebeing normally positioned with said cavity, aperture and opening inalignment, a true shear plane being defined at an interface between thespindle and ring means and a false shear plane being defined at aninterface between the ring means and housing; d. a tumbler assemblycomprising a first pin positioned in said cavity, said first pin havingan outer end normally positioned at said false shear plane, a second pinnormally positioned in said opening with an inner end thereof normallyin contact with said first pin at said faLse shear plane and an outerend thereof normally within said aperture, a third pin normallypositioned in said aperture with an inner end thereof normally incontact with said second pin, the third pin being accessible to a keyfrom without the housing, the second pin normally preventing relativerotational movement between the spindle and ring, and means for biasingsaid tumbler assembly to its normal position; e. means for allowing onlya limited rotation of the ring means relative to the housing, whichlimited rotation is sufficient in extent to effect a misalignment of theopenings in the ring with the cavities in the housing; and f. means forenabling substantially unrestrained axial movement of said third pin atleast part of the way into the opening of said ring means.
 2. A pickresistant lock comprising: a. a hollow housing having an elongate cavityformed therein; b. a spindle rotatably mounted within said housing andincluding an aperture extending therethrough at a location thereon foralignment with said cavity; c. ring means rotatably mounted about thespindle between the spindle and the housing and including an openingextending therethrough at a location thereon for alignment with saidcavity and said aperture, the ring means and spindle being normallypositioned with said cavity, aperture and opening in alignment, a trueshear plane being defined at an interface between the spindle and ringmeans and a false shear plane being defined at an interface between thering means and housing; d. a tumbler assembly comprising a first pinpositioned in said cavity, said first pin having an outer end normallypositioned at said false shear plane, a second pin normally positionedin said opening with an inner end thereof normally in contact with saidfirst pin at said false shear plane and an outer end thereof normallywithin said aperture, a third pin normally positioned in said aperturewith an inner end thereof normally in contact with said second pin, thethird pin being accessible to a key from without the housing, the secondpin normally preventing relative rotational movement between the spindleand ring, and means for biasing said tumbler assembly to its normalposition; e. means for allowing only a limited rotation of the ringmeans relative to the housing, which limited rotation is sufficient inextent to effect a misalignment of the openings in the ring with thecavities in the housing; and f. wherein the cavity, aperture and openingeach extend elongately in a direction parallel to the longitudinal axisof the housing.
 3. The lock of claim 1, wherein the enabling meansincludes the inner end of said third tumbler pin being chamfered to anouter diameter substantially less than the diameter of said opening.